Eur J Appl Physiol (1988) 57:230--234

European Journal of

Applied Physiology and Occupational Physiology �9 Springer-Verlag 1988

The responses of the catecholamines and fl-endorphin to brief maximal exercise in man

Stephen Brooks 1, Jacky Burrin 2, Mary E. Cheetham 1, George M. Hall 2, Tom Yeo 2, and Clyde Williams 1

t Department of Physical Education and Sports Science, University of Technology, Loughborough, Leicestershire LE11 3TU, Great Britain

2 Departments of Medicine and Anaesthetics, Royal Postgraduate Medical School, Hammersmith Hospital, London W12 0HS, Great Britain

Summary. The responses to brief maximal exer- cise of 10 male subjects have been studied. Dur- ing 30 s of exercise on a non-motorised treadmill, the mean power output (mean+SD) was 424.8+41.9 W, peak power 653.3+103.0 W and the distance covered was 167.3+9.7m. In re- sponse to the exercise blood lactate concentra- tions increased from 0.60+0.26 to 13.46+1.71 mmol. 1- ] (p < 0.001) and blood glucose concen- trations from 4.25+0.45 to 5.59+0.67 mmol.1-1 (p<0.001). The severe nature of the exercise is in- dicated by the fall in blood pH from 7.38 + 0.02 to 7.16+0.07 (p<0.001) and the estimated decrease in plasma volume of 11.5+3.4% (p<0.001). The plasma catecholamine concentrations increased from 2.2+0.6 to 13.4+6.4 nmol. l - ] (p<0.001) and 0.2+0.2 to 1.4_+0.6 nmol.1 -~ (p<0.001) for noradrenaline (NA) and adrenaline (AD) respec- tively. The plasma concentration of the opioid fl- endorphin increased in response to the exercise from <5.0 to 10.2+_3.9 p mol.1 -~. The post-exer- cise AD concentrations correlated with those for lactate as well as with changes in pH and the de- crease in plasma volume. Post-exercise r phin levels correlated with the peak speed at- tained during the sprint and the subjects peak power to weight ratio. These results suggest that the increases in plasma adrenaline are related to those factors that reflect the stress of the exercise and the contribution of anaerobic metabolism. In common with other situations that impose stress, fl-endorphin concentrations are also increased in response to brief maximal exercise.

Key words: Exercise -- Catecholamines -- fl-en- dorphin -- Blood glucose -- Blood lactate

Offprint requests to: C. Williams at the above address

Introduction

Exercise has been shown to change the plasma concentrations of many hormones. However, the majority of studies have involved exercise of a long duration (see Galbo 1983) whilst the re- sponses to brief maximal exercise have received little attention. Moreover, in those cases where hormonal responses to brief maximal exercise have been studied the responses are often differ- ent from those observed in prolonged exercise (N~ivari et al. 1985).

The release and rate of release of hormones are controlled in response to specific needs. The rates of secretion should thus be related to their metabolic functions and the needs of a particular circumstance. The increase in sympathetic activity with exercise has been shown to influence muscle and liver glycogenolysis (Galbo 1983) to provide the glucose for further energy production. The natural opioid fl-endorphin has also been shown to increase with exercise (Farrell 1985). The meta- bolic consequences of raised circulating fl-endor- phin levels are unclear although a wide range of possible affects have been proposed (Allen 1983). Whilst in prolonged exercise hormonal responses appear to be related to the relative intensity of the exercise, what influences the quantitative re- sponses to brief maximal exercise is not known.

We have used a 30 s sprint on a non-motorised treadmill (Cheetham et al. 1986), to investigate the responses of the catecholamines and/3-endorphin to brief maximal exercise.

Methods

Ten male subjects volunteered for these experiments which had University Ethical committee approval. The subjects,

S. Brooks et aL : Catecholamines and fl-endorphin in brief maximal exercise 231

whose age ( m e a n + S D ) was 32.3+10.6 years and weight 71.3 _+ 6.9 kg, had previous experience of the experimenta! pro- cedure and were a physically active group with a mean Vo ...... of 59.5+7.1 m l . k g - ~ . m i n -1. The maximal exercise test in- volved a sprint of 30 s duration on a non-motorised treadmill. The performance of the test was monitored by recording the treadmill belt speed and the horizontal component of the force exerted by the subjects on the belt enabling force, speed, power and distance to be determined (Lakomy 1987). The heart rate of all subjects was monitored throughout the experi- ment.

The experimental procedure involved a standardised warm-up on the treadmill of two 30 s periods at 2.2 and 2.8 m. s - '. This was followed by 5 min of rest in a recumbent po- sition after which, a venous blood sample (20 ml) was taken from an antecubital vein. The sprint, which began from a roll- ing start at 2.2 m.s ~, involved the subjects accelerating the treadmill to their maximum abilities and attempting to main- tain this speed for 30 s. After the sprint, the subjects returned to the recumbent position where mixed arterialised samples (20 l.tl) were taken from the thumb at 1 and 5 rain post-exercise and a venous sample taken 3 min post-exercise. Further ve- nous samples were taken from 4 of the subjects 10 and 20 min post-exercise.

Venous samples were analysed for blood pH immediately following collection. Four aliquots were then taken, two of which, with the mixed arterialised samples, were analysed for glucose and lactate by enzymatic methods (Maughan 1982). The second two were used to determine blood haemoglobin and haematocrit values in order to calculate the percentage change in plasma volume (Dill and Costill 1974). The remain- ing blood was centrifuged at 3~ and the plasma stored at - 2 5 ~ after the addition of 200 Ixl of an anti-oxidant solution (100 retool. 1- ~ of reduced glutathione and EGTA adjusted to pH 6.5). Plasma catecholamines were determined by HPLC using electrochemical detection (Davies et al. 1981).

Plasma immunoreactive fl-endorphin concentrations were determined using a two step assay, fl-endorphin was first ex- tracted from the plasma sample using Sepharose linked rabbit anti-fl-endorphin antibodies. The bound fraction was eluted and assayed by a radioimmunoassay for fl-endorphin. Cross reactivity with N-acetyl fl-endorphin was 100%, with/Mipotro- pin < 5% and with ACTH <0.01% (Immuno Nuclear Corpo- ration, Stillwater, Minnesota, USA). The minimum detectable plasma B-endorphin concentration was 5 pmol-1 - 1.

The statistical evaluation of the results was carried out us- ing the Pearson product-moment correlation, a Student 's t-test for paired data or where stated a Mann-Whitney test.

tO

0

!

10 20 30

Time Is]

Fig. 1. The belt speed during a 30 s sprint on a non-motorised treadmill (n = 10, mean + SD)

I/o2 .... . Of the ten subjects, the maximum heart rate of eight was recorded between 10 and 20 s after the sprint rather than during the sprint itself. Blood pH fell from a pre-exercise value of 7.38+0.02 to 7.16_+0.07 after the sprint, a mean fall of 0.23 whilst plasma volume fell by 11.5_+3.4%. The increases in blood lactate and glucose are shown in Table 2. Plasma AD and NA concentrations also increased in response to the sprint, there being a 7 fold increase in AD from 0.2_+0.2 to 1.4+0.6 nmot . l -1 and a 6 fold in- crease in NA from 2.2_+0.6 to 13.4-+6.4 nmol-1 -

Table 1. Performance results of a 30 s sprint on a non-moto- rised treadmill (n=10) . Fatigue is expressed as the (peak speed - end speed) /peak speed* 100

Mean SD

Peak power (W) 653.3 103.0 Peak power /Wt (W. k g - ' ) 9.2 1.4 Mean power (W) 424.8 41.9 Peak speed (m- s - 1) 6.4 0.3 Distance (m) 167.3 9.7 % fatigue 22.8 6.5

Results

The performance results for the 30 s sprint, as re- flected by the treadmill belt speed, are shown in Fig. 1. This shows the initial acceleration from a rolling start, to reach a maximum speed after 4.7 + 1.5 s and the subsequent decline in speed as fatigue occurs. The results of the other aspects of performance measured are shown in Table 1.

The maximum heart rate reached during the 30 s was 173 + 13 beats per minute however, this was not as high as the 188 +9 beats per minute (p <0.001) attained during the incremental grade test on a motorised treadmill used to determine

Table 2. Blood glucose and lactate concentrations in venous samples (pre and 3 min post) and mixed arterialised samples (1 and 5 min post) before and after a 30 s sprint on a non- motorised treadmill ( n = 10, *p<0.001 paired t test, post vs pre)

Pre Post

1 min 3 min 5 min

Glucose mean 4.25 5.22 5.59. 6.05 (mmol. 1 ~) SD 0.45 0.72 0.67 0.76

Lactate mean 0.60 11.I0 13.46. 15.56 (mmol-1-1) SD 0.26 1.16 1.71 1.69

232 S. Brooks et al.: Catecholamines and/%endorphin in brief maximal exercise

The pre-exercise concentrations of /3-endor- phin in plasma were below the limits of sensitivity of the assay (less than 5.0 pmol.l-1, the mean resting value calculated from data reviewed in Farrell (1985) was 3.2 + 1.5 pmol- 1-1). However, the levels increased by at least 2 fold as the mean post-exercise concentration was 10.2 _+ 3.9 pmol. 1-1.

In the 4 subjects from whom further samples were taken, fl-endorphin concentrations fell to 8.6+1.7 pmol.1-1 after 10min and 5.5+1.0 pmol.1-1 after 20 min (see Fig. 2). A comparison of these results with those of the 10 subjects (Mann-Whitney test) indicated that there was no fall in/%endorphin concentrations after 10 rain but that a significant fall had occured by 20 rain post-exercise (p < 0.05).

Correlations were found between post exer- cise AD levels and both post exercise blood lac- tate (r= 0.701,p <0.05) and blood pH (r= -0.708, p<0.05). A correlation was also found between the percentage decrease in plasma volume and the post exercise AD (r = 0.690, p < 0.05). The post-ex- ercise plasma concentrations of/%endorphin were related to the decrease in blood pH ( r = - 0.620, p < 0.05) and to two aspects of the performance of the sprint. The correlation between/%endorphin and the peak power to weight ratio of the subjects being r=0.808 (p<0.01) and the peak speed the subjects attained being r=0.708 (p<0.05) (see Fig. 3).

20"

o o E E ,:. ~Io

z & <5

Pre Post

[]

[]

il J 10 20

Time Post [min]

AD

NA

~-END

Fig. 2. Plasma AD, NA and fl-endorphin concentrations (mean_+ SD) before and after a 30 s sprint on a non-motorised treadmill (*p<0.001 for paired t test p r e v s post where n = 10 and + p < 0 . 0 5 for Mann-Whitney test post vs 10 and 20 rain post where n = 10 and 4)

15- i

o E

IO- z

5-

o

o o

o o o

o

o o

o ~

o

8 o

o o

6.5 7 8 IO 12

Peak Speed Peak Power/Weight [m.s-1] [W.k9-1 ]

Fig. 3. The correlations between the post-exercise fl-endorphin levels and the peak power to weight ratio (r=0.808, p<0 .05) and the peak speed (r=0.708, p<0.05) for a 30 s sprint on a non-motorised treadmill (n = 10)

D i s c u s s i o n

The intensity of the exercise during the 30 s sprint is evident from the 22 fold rise in the concentra- tion of blood lactate. These high levels reflect the large contribution made by anaerobic metabolism and represent the utilisation of about 25% of the available skeletal muscle glycogen stores in just 30 s (Cheetham et al. 1986).

Circulating levels of AD and NA increased in response to the exercise test, the magnitude of the responses being similar to those after 30 s of max- imal exercise on a cycle ergometer (MacDonald et al. 1983). During graded exercise the increases in the catecholamines appear to be related to the in- tensity as measured by Vo ..... and to the duration of the exercise (Lehmann et al. 1983). The factors influencing catecholamine concentrations in re- sponse to brief maximal exercise are less clear. Variations in sympathetic tone will affect levels of AD and NA released from the adrenal medulla. One of the factors that has been shown to in- fluence the central control of sympathetic tone is a change in muscle osmolarity and/or potassium (Tibes et al. 1976). Interestingly, in the present study a correlation was found between post-exer- cise AD and the decrease in plasma volume. With sustained muscle contraction, vascular sympa- thetic nerve activity increases in proportion to the tension developed (Saito et al. 1986). If this also occures in dynamic exercise, then changes in the amount or degree of sympathetic innervation should be reflected by variations in the overflow of the transmitter NA into the circulation.

Differences in the response to maximal exer- cise have been demonstrated between individuals with different training backgrounds. Ohkuwa et al. (1984) have shown that a sprint trained group of runners had higher AD, NA and lactate c o n -

S. Brooks et ai.: Catecholamines and fl-endorphin in brief maximal exercise 233

centrations after performing a 400 m sprint than an untrained group of subjects, even though the duration of the exercise was longer for the un- trained group. They proposed that the differences in fibre types between the groups may contribute to the variations in lactate, the sprint group hav- ing a greater proportion of fast twitch (glycolytic) fibres. The findings in the present experiments of correlations between post-exercise concentrations of lactate and AD and between AD and blood pH would be consistent with this view. In addition, a correlation between circulating AD and degree of glycolysis has been demonstrated for female sub- jects undertaking this same type of high intensity exercise (Cheetham et al. 1986).

The post-exercise hyperglycaemia seen in the present study can not be explained by changes in plasma volume. The magnitude of the change in blood glucose being over twice that of the change in plasma volume (32% and 11.5% respectively). The experiments of Lavoie et aL (1987) have indi- cated that liver glycogenolysis is responsible for the post-exercise increase in glucose after brief supramaximal exercise. The post-exercise concen- trations of AD and NA are such that direct stimu- lation should occur even though an increase in glucagon has also been demonstrated (N~iveri et al. 1985).

Whilst catecholamine concentrations have been shown to be related to the exercise intensity (as % l)'o ..... , Lehmann et al. 1983), fl-endorphin concentrations do not appear to be related to the intensity of exercise as measured by I2o2 . . . . . (re- viewed in Farrell 1985). Inter-individual varia- tions in responses have been demonstrated and De Meirleir et al. (1986) have proposed that both metabolic and hormonal influences affect fl-en- dorphin release. These increases in circulating ca- techolamines and fl-endorphin may not be disso- ciated. In rats, f12 agonists produce a dose depend- ent increase in circulating fl-endorphin (Berken- bosch et al. 1981). Influence in the opposite direc- tion is seen in man where naloxone augments the exercise induced increase in circulating AD and NA (Grossman et al. 1984). The fl-endorphin re- sponse to brief maximal exercise (mean post-exer- cise plasma levels 10.2 pmol-l-~) was lower than most reported post-exercise value (see Farrell 1985). However, the duration of the exercise in all these cases was longer than the 30 s used in the present study. Thus, duration would appear to be one factor in determining the magnitude of the fl- endorphin response. In the present study correla- tions were found between post-exercise fl-endor- phin concentrations and two measurements of

performance, the peak power to weight ratio and peak speed (see Fig. 3). Thus, higher peak speeds or higher peak power to weight ratios correspond to higher post-exercise fl-endorphin levels. This relationship is supported by the finding that a training regimen that improved performance also increased fl-endorphin release (Carr et al. 1981).

In summary, the present study contributes to a description of the fl-endorphin response to exer- cise and the demonstrates that brief maximal ex- ercise will increase circulating concentrations. However, the role of fl-endorphin in exercise is unclear and requires further investigation.

Acknowledgement. This work was funded by the Sports Coun- cil of Great Britain.

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Accepted August 14, 1987